1. Field of the Invention
The present invention relates to a plastic made, rectangular airtight container for food.
2. Related Art
As a container for housing and storing food, a plastic made airtight container 101 as shown in FIG. 4 to FIG. 6 is widely used.
This plastic made airtight container 101 consists, of container main body 103 and lid 102, a plurality of locking projections 110 projected at top portion of the container main body 103, and locking wing pieces 105 which are folded and unfolded around hinge 106. The wing pieces rotatively move around hinge 106 which are formed integrally with the top lid surface 104 of the lid 102. Locking holes 107 are inserted and locked to locking projections 110 formed to lock with the wing pieces 105 at a position corresponding to each locking projection 110.
A recess 111 is formed in the top lid surface 104 of lid 102 which is adapted to engage with the top edge 113 of the container main body 103. A packing 112 can be inserted into groove 111.
Accordingly, when the lid 102 is placed on the container main body 103 and a finger pressing portion 105a is pressed by a finger, i. e., when the locking wing piece 105 is pressed toward the locking projection 110 of the container main body 103, the locking projections 110 are locked by passing them through locking holes 107a nd 107b, respectively. Since the top edge 113 presses against the packing 112, the interior space 114 of the container main body 103 is hermetically sealed from the exterior.
However, in accordance with above described airtight container 101, the locking wing piece 105 is connected by a hinge 106 which is decreased very much in thickness, and since the hinge 106 has to be folded and unfolded by the locking wing piece 105, a bending stress is repeatedly produced and therefore is very weak.
On the other hand, as shown in drawings, in the case of an elongated rectangular airtight container 101, and in the case where the length of one side is more than 10 cm, the locking hole 107 of the locking wing piece 101 and the locking projection 110 of the container main body 103 are made to be two on each side so as to secure a sufficient locking force and a uniformity of the hermetical sealing force (airtight force).
In the case of a rectangular airtight container 101 with a lid 102, since a plastic molten liquid pouring gate 115 is formed to an injection metal mold corresponding to the right center of the lid 102, in the process in which the plastic molten liquid spreads out in every direction from the molten liquid pouring gate 115 and fills up the cavity of metal mold by which the lid 102 is made, the traveling time in which the plastic molten liquid is spread to each end terminal portion of the mold is different, and since the molten liquid flows in counter current directions to itself, collisions of the molten liquid forms weld lines, and strength weakened portions.
Since both end terminal portions 105b of the locking wing piece 105 are most distanced from the molten liquid pouring gate 115 whereby the molten liquid traveling time is the longest, and since the gorge portion 105b is formed due to the locking hole 107, the gorge portion 105b operates as a resistive means for the flow of molten liquid, whereby the flow of the molten liquid flow becomes stagnated. On the other hand, for a center portion between both side locking holes 107, since the distance from the molten liquid pouring gate 115 is closer and the clearance is greater and the flowing resistance is less, the flow of molten liquid becomes smooth whereby the flow of molten liquid occurs as shown by arrows. Thus, the molten liquid collides with itself at the hinge end portion 106a which is the end terminal portion of the hinge 106, thereby forming a weld line. (Generally the weld line is formed at the hinge end terminal portion at a rate of 5-15%).
When a weld line is formed by the collision of the molten liquid, at the hinge end portion 106a, a thin hinge end portion 106a forms a cracked portion which is easily torn out and damaged when locking the wing piece portion 105 is repeatedly folded and unfolded. Once the hinge end portion 106a is torn out, even just a little, it continuously spreads out whereby the life of the airtight container 101 is considerably decreased, and this dissatisfaction of the consumer has been pointed out as a significant problem. Since this inferiority of product cannot be confirmed at manufacturing state, and since the problem would appear only after a predetermined time is past while the consumer is using the product (but in a further short time than regular life of the product), this problem is a big issue for consumer protection.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.